1. Field of the Invention
This invention relates generally to a muffler for quieting the exhaust from an internal combustion marine engine, and more particularly, to a muffler whose inlet is opposed to the direction of backflowing surge water.
2. Description of the Prior Art
The exhaust of the typical inboard marine vessel is directed through the transom. Such applications place the exhaust outlet near or below the water line leading to possible back flow situations when the exhaust gas does not present enough force to overcome a water surge, or where water enters the exhaust pipe while the engine is off. To prevent this back flow of water into the muffler or engine, a check valve or flapper valve is usually employed. Additionally, as shown in FIG. 1, in a typical prior art exhaust system a surge pipe may be employed such that the engine output is elevated with respect to the exhaust outlet thereby decreasing the possibility of back flow entering the marine engine. However, none of the prior art muffler designs have an attenuation chamber with an inlet that is opposed to the direction of backflowing surge water. Rather, the present state of the art flapper valves, having moving parts which quickly corrode and fail, leading to either a potentially dangerous blockage of exhaust flow or an open ended exhaust pipe that makes a marine engine more susceptible to backflowing surge water.
There are a variety of marine mufflers presently known in the art which are of the "axial flow" type such as the muffler disclosed in U.S. Pat. No. 4,167,987, issued to Turner. The Turner patent describes a multiple flow marine muffler wherein exhaust noise is attenuated by passing the exhaust gas through a series of longitudinally spaced opposing baffles. However, such a configuration requires an elongated cylindrical shell to provide the required baffling effect, thus precluding application in tight-fit areas such as smaller boats or other situations where space is at a premium. Additionally, the use of an axial flow muffler cannot be placed below the water line without some form of surge suppression.
Another marine muffler, known as a "lift muffler," is disclosed in U.S. Pat. No. 3,296,997, issued to Hoiby, et al. The Hoiby muffler is essentially an up-right drum-shaped housing having an exhaust inlet near the top and a stand pipe exhaust outlet centrally located with its opening spaced above the drum bottom. The stand pipe directs the muffled exhaust gas and collected cooling water upwardly and outwardly to a location where it can be discharged from the boat without further back pressure. However, Hoiby does not present a means to prevent a reverse flow of water when the exhaust outlet is submerged. Additionally, such a device precludes application in tight-fit areas as the centrally located stand pipe requires exhaust conduit modifications to accommodate the pipe.
The exhaust outlet of an inboard-powered marine vessel is usually placed at or about the water line of the boat. As a result, surges of water routinely enter the exhaust outlet and travel through the exhaust system. This surge water could disable the engine if it is permitted to travel far enough, possibly leading to disastrous results, especially if the vessel is far from port. No one has heretofore proposed a reverse entry anti-surge marine muffler in which exhaust flow and collected coolant enters the muffler against the direction of flow of the outlet stream.
Therefore, there exists a need for a muffler capable of replacing a conventional muffler and surge pipe wherein the exhaust inlet is angled such that exhaust flow enters the muffler against the direction of flow of the outlet stream and hence inhibits back flow into a marine engine without the addition of moving parts such as a check or flapper valve.